1. Field of the Invention
The disclosed invention relates generally to monitoring photolithography processing, and more specifically to monitoring changes in photolithography processing that occur due to a change in the batch of light sensitive material applied to a substrate.
2. Discussion of the Background
In material processing methodologies, pattern etching includes the application of a thin layer of light-sensitive material, such as photoresist, to an upper surface of a substrate that is subsequently patterned in order to provide a mask for transferring this pattern to the substrate during etching. The patterning of the light-sensitive material is typically referred to as photolithography processing and generally involves coating an upper surface of the substrate with a thin film of light-sensitive material, exposing the thin film of light-sensitive material to a radiation source through a reticle (and associated optics) using, for example, a micro-lithography system, followed by a developing process during which the removal of the irradiated regions of the light-sensitive material occurs (as in the case of positive photoresist), or the removal of non-irradiated regions occurs (as in the case of negative resist) using a developing solvent. As a result, a desired resist pattern is formed on the substrate. After a desired resist pattern is formed on the substrate, the wafer is transferred to an etching apparatus where an etching process is performed as a next step to transfer the resist pattern into the substrate.
Recently, the resist and etch patterns formed upon a substrate are required to be finer, and a severe control upon the line width of the resist and etch patterns has become inevitable. Thus, inspection of resist patterns on a substrate is typically carried out by a worker measuring a critical dimension (CD) of the resist pattern on the surface of a substrate brought out from the resist coating and developing system, with a Scanning Electron Microscope (SEM), and judging whether the measured value of the line width satisfies the required standards. These “CD-SEM” measurements can be used to make corrections to exposure energy, for example, in an effort to ensure that photoresist patterns meet target CDs. Similarly, strict inspection and control techniques are used to ensure that subsequent etch results are consistent with target resist patterns.
Despite these inspection and control efforts, however, a post-etch inspection can reveal a sudden change in measured CD of the etched feature. While the photolithography process and/or etch process may be modified to bring the CD back into tolerance, several wafers may be scrapped before the CD shift is detected and corrected, resulting in reduced product yield.